'\" et
.TH SOCKET "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
socket
\(em create an endpoint for communication
.SH SYNOPSIS
.LP
.nf
#include <sys/socket.h>
.P
int socket(int \fIdomain\fP, int \fItype\fP, int \fIprotocol\fP);
.fi
.SH DESCRIPTION
The
\fIsocket\fR()
function shall create an unbound socket in a communications domain, and
return a file descriptor that can be used in later function calls that
operate on sockets. The file descriptor shall be allocated as described in
.IR "Section 2.14" ", " "File Descriptor Allocation".
.P
The
\fIsocket\fR()
function takes the following arguments:
.IP "\fIdomain\fR" 12
Specifies the communications domain in which a socket is to be
created.
.IP "\fItype\fR" 12
Specifies the type of socket to be created.
.IP "\fIprotocol\fR" 12
Specifies a particular protocol to be used with the socket. Specifying
a
.IR protocol
of 0 causes
\fIsocket\fR()
to use an unspecified default protocol appropriate for the requested
socket type.
.P
The
.IR domain
argument specifies the address family used in the communications
domain. The address families supported by the system are
implementation-defined.
.P
Symbolic constants that can be used for the domain argument are defined
in the
.IR <sys/socket.h> 
header.
.P
The
.IR type
argument specifies the socket type, which determines the semantics of
communication over the socket. The following socket types are defined;
implementations may specify additional socket types:
.IP SOCK_STREAM 12
Provides sequenced, reliable, bidirectional, connection-mode byte
streams, and may provide a transmission mechanism for out-of-band
data.
.IP SOCK_DGRAM 12
Provides datagrams, which are connectionless-mode, unreliable messages
of fixed maximum length.
.IP SOCK_SEQPACKET 12
.br
Provides sequenced, reliable, bidirectional, connection-mode
transmission paths for records. A record can be sent using one or more
output operations and received using one or more input operations, but
a single operation never transfers part of more than one record. Record
boundaries are visible to the receiver via the MSG_EOR flag.
.P
If the
.IR protocol
argument is non-zero, it shall specify a protocol that is supported by
the address family. If the
.IR protocol
argument is zero, the default protocol for this address family and type
shall be used. The protocols supported by the system are
implementation-defined.
.P
The process may need to have appropriate privileges to use the
\fIsocket\fR()
function or to create some sockets.
.SH "RETURN VALUE"
Upon successful completion,
\fIsocket\fR()
shall return a non-negative integer, the socket file descriptor.
Otherwise, a value of \-1 shall be returned and
.IR errno
set to indicate the error.
.br
.SH ERRORS
The
\fIsocket\fR()
function shall fail if:
.TP
.BR EAFNOSUPPORT
.br
The implementation does not support the specified address family.
.TP
.BR EMFILE
All file descriptors available to the process are currently open.
.TP
.BR ENFILE
No more file descriptors are available for the system.
.TP
.BR EPROTONOSUPPORT
.br
The protocol is not supported by the address family, or the protocol is
not supported by the implementation.
.TP
.BR EPROTOTYPE
The socket type is not supported by the protocol.
.P
The
\fIsocket\fR()
function may fail if:
.TP
.BR EACCES
The process does not have appropriate privileges.
.TP
.BR ENOBUFS
Insufficient resources were available in the system to perform the
operation.
.TP
.BR ENOMEM
Insufficient memory was available to fulfill the request.
.LP
.IR "The following sections are informative."
.SH "EXAMPLES"
None.
.SH "APPLICATION USAGE"
The documentation for specific address families specifies which
protocols each address family supports. The documentation for specific
protocols specifies which socket types each protocol supports.
.P
The application can determine whether an address family is supported by
trying to create a socket with
.IR domain
set to the protocol in question.
.SH "RATIONALE"
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "Section 2.14" ", " "File Descriptor Allocation",
.IR "\fIaccept\fR\^(\|)",
.IR "\fIbind\fR\^(\|)",
.IR "\fIconnect\fR\^(\|)",
.IR "\fIgetsockname\fR\^(\|)",
.IR "\fIgetsockopt\fR\^(\|)",
.IR "\fIlisten\fR\^(\|)",
.IR "\fIrecv\fR\^(\|)",
.IR "\fIrecvfrom\fR\^(\|)",
.IR "\fIrecvmsg\fR\^(\|)",
.IR "\fIsend\fR\^(\|)",
.IR "\fIsendmsg\fR\^(\|)",
.IR "\fIsetsockopt\fR\^(\|)",
.IR "\fIshutdown\fR\^(\|)",
.IR "\fIsocketpair\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<netinet_in.h>\fP",
.IR "\fB<sys_socket.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
